A. Field Of The Invention
The present invention relates to a new and improved valve and particularly, to a new and improved cold box valve including a unitized trim assembly with a valve seat ring and a spring and retainer assembly biasing the trim assembly and the valve seat ring into engagement with an opening between the inlet and outlet of the valve.
B. Description Of The Background Art
Cold box valves are employed in control systems that handle fluids at cryogenic temperatures. These fluids, such as liquid nitrogen, are typically at temperatures as low as -320.degree. F. The valves are mounted at a 15.degree. angle to the horizontal and are elongated. In this environment, the valve can be simultaneously subjected at the upper end to ambient temperatures and at the lower end to temperatures as low as -320.degree. F. In these valves, the seal is located at the lower end and experiences drastic variances in temperature. For example, in the open position while liquid nitrogen is flowing through the valve, the temperature can be -320.degree. F. Once the valve is closed, after two or three hours the lower end of the valve and valve seal return to approximately ambient temperature. It is desirable that the valve seat ring and seal be maintained in sealing engagement over these widely varying temperatures. It is also desirable that the seat ring and seal are easily repaired or replaced. Since the valve seat ring and seal are located at the lower end of the valve and the typical cold box valve includes a long extension or neck, servicing of the valve seat ring and seal is often extremely difficult and sometimes impossible necessitating complete removal and disassembly of the valve. If the valve can be disassembled and the valve seat ring and seal replaced, reassembly is often difficult since several separate parts must be properly positioned within the valve. Existing cold box valves include seals or gaskets that are separate parts and must be assembled prior to final assembly of the valve. An example of a valve that must be completely disassembled in order to remove and replace the valve seat and seal is illustrated in U.S. Pat. No. 3,206,165. The separate components of the valve illustrated in this patent are difficult to disassemble and reassemble particularly if the valve is installed in a system such as a cryogenic fluid line.